D.N. LAPSHIN, D.D. VORONTSOV
FREQUENCY TUNING OF THE HEARING SYSTEM OF NOCTUID MOTHS (LEPIDOPTERA, NOCTUIDAE) DURING FLIGHT
Noctuid moths Amphipyra pyramidea L. and Crino satura Schiff.under conditions of tethered flight were stimulated with short (2.5 ms) acoustic pulses which were presented synchronously with wingbeats. Behavioural thresholds were investigated depending on filling frequency of pulses in range from 2 to 100 kHz and the wingbeat phase at the moment of stimulation. It was shown that behavioural audiograms essentially differ in shape and minimal thresholds from those of tympanic organ which were obtained earlier in acute experiments. In particular, the decrease of thresholds analogous to the tympanal resonance was observed only in a narrow part of wingbeat cycle: wing's downward movement from it's horizontal position to the lower point. In all other cases there were not any noticeable areas of increased sensitivity in audiograms - the thresholds were increasing smoothly to the terminal points of the frequency range. From 2 to 10 kHz there were the maximal thresholds at 5 kHz and the minimal ones at 3 kHz in all specimen studied. The peculiarity of moths' behavioural characteristics can be accounted for cyclic shifts of tympanal resonance which may originate from pressure changes in tympanic cavity and/or stretches of the membrane by adjoining structures.
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